Hollywood Bowl - July 21,1974

The Grateful Dead sound system is really 11 independent systems or channels. The source of sound are located behind and above the performers so they hear what the audience hears. Only one source location for each channel is used to cover the entire hall and the music is clearer both on stage and in the audience. The stereo effect is very satisfying and natural to persons all over the hall. Intermodulation distortion between instruments is of course non-existant.

Excessive reverberation and echos often impair the sound quality when performing in sports arenas. These buildings often sound worse than simple observation of reverberation times might indicate due to troublesome wall surfaces creating echoes. Conventional systems which have multiple sources for each sound add additional delays. The result is a confusing sound which causes the musicians and sound system operators to turn up the level in an effort to overcome this muddle of sound by the limiting effect of the ear. The Grateful Dead system with its single source for each instrument projects clear sound farther back into these cavernous nightmares, and since the sound from each instrument comes from a different direction, the echoes are more diffuse and therefore less objectionable.

Conventional systems are set up low to the ground and the major energy is projected straight back where it strikes the rear wall and is reflected back to the musicians with a delay approaching a half-second. Extremely high stage monitor levels are required to overcome this echo and musicians often comment that they can't hear well but that the high level hurts their ears. The low angle of aim also causes additional reflections from side and front walls which detract from clarity in the audience area. In the Dead's system the source of sound is higher and aimed down. The original sound is partly absorbed by the audience and the first reflection from the real wall is directed down into the audience for further absorption. In this way, the apparent reverberation is substantially reduced, and this effect is significant when the only absorptive material in a reinforced concrete enclosure is the audience.

Conventional monitor systems may not be aimed at any absorptive surface and may operate only four to six dB lower in radiated energy than the house system. This can cause a substantial increase in the apparent reverberation of a hall with a reflective ceiling. Conventional systems sometimes sound satisfactory in these halls when reproducing recorded music at intermissions with the stage monitors turned off, but sound confused and jumbled during the live portions of the program. The Dead's system has no comparable monitoring energy and avoids this increase in reverberation.

Conventional systems suffer from an interference effect due to path differences between sources carrying coherent information. Since the effect is fixed, a "filtered" quality is imparted to the sound instead to the sound instead of the swishing phasing sound used in recordings as a special effect. In outdoor concerts however, the swishing effect is very audible due to differing path lengths caused by changes in atmospheric conditions. In either case, the effect is detrimental and in the Dead's system, the single source for each instrument gives very pleasant "acoustic" or natural sounding music.

To assure good articulation and naturalness the vocal system is designed along the lines of establishing good practice for sound reinforcement systems. But for the instrument systems. deviations are desirable in certain cases for musical reasons. Many acoustic instrument are not designed to give good coverage to every seat in the house but an orchestra sounds good in a symphony hall. In the Dead's system, the array for each instrument is experimentally adjusted to achieve the musical effect the performers desires. We found the piano system to need conventional standard coverage, and its array resembles the vocal system. For the guitars a more a more reverberate sound is desired, and energy is directed around the hall, artificial reverberation is added and digital time delay is used in certain compositions to change the sound of the instruments. In the mid bass region, the halls are generally muddy and here we have used a more directional array than is usual for the bass guitar and have achieved a very clear, distinct bass sound. Parts of the system are also used with electronic music synthesizers in conjunction with the bass guitar and a digital computer "an organic artificial musical intelligence."

When work on the system resumes, many interesting directions are under consideration. The availability of low cost delay electronics makes it possible to design a phased array where the energy form the source can be aimed by adjusting controls. We now use physical tilting of the entire array but the sheer bulk of the system makes the cost of this operation prohibitive for every performance. The ability to electronically direct the sound would make a better adaptation of the system to every situation. The possibility to dynamically change the directionality as a musical effect is interesting. The design of multi-way arrays for the guitars and bass is contemplated. Additional channels for voice and drums will be added to further carry out the separate source approach. Improvements will be made to the drum system pickup with microphone development and exploration of accelerometer transducers. The work with computer assisted and synthesized music will continue.

The system represents the efforts of many people. I would particularly like to recognize Owsley "Bear" Stanley whose intuition we have followed and who is the essential catalyst for the system's development. Also, John Curl contributed elegant electronics designs and Rick Turner of Alembic, and Dan Healy and the Grateful Dead Road Crew who worked so hard to make the system realizable.

The whole system operates on 26,400 Watts of continuous (RMS) power, producing in the open air quite an acceptable sound at a quarter of a mile and a fine sound up to five or six hundred feet, where it begins to be distorted by wind, A sound system could get the same volume from half as much power, but it wouldn't have the quality

Note: the amplifiers used were all identical dual channel 300 watts per channel solid state type with matching transformers except for one each in the vocal and drum system which were Tube type at 350 watts, and operated the tweeters.

The Vocal System

The signals from each of the vocal microphones are brought together by a differential summing amp, where phase purity can be regulated and hence the transparency of sound maintained. From there the combined signal goes to a crossover which divides the frequency range into four band (High, Upper Mid, Lower Mid, Low). The signal in each band is then separately amplified by MacIntosh 2300 amps fed to JBL 15 inch, 12 inch, 5 inch or Electrovoice tweeters.

The center cluster of the vocal system, consisting of high and midrange speakers, is curved so as to disperse sound cylindrically; there is not much vertical dispersion, and horizontal dispersion is ideally between 140 and 180 degrees. The vocal low range speakers are arranged in a column, Each type of speaker is designed to have the same horizontal and vertical dispersion so that all frequencies are heard equally well.

The speaker cones are arranged together as close as possible so that the whole surface of the cluster acts as one working surface. In this way a large mass of air is moved at once which doesn't require high pressure from any individual speaker

A major improvement in the quality of the vocal sound is due to the use of differential microphones. Each singer has a perfectly matched pair of Bruel and Kjaer microphones hooked up out if phase, only one of which he sings into. Any sound which goes equally into both microphones is canceled out when the two signals are added together. Therefore leakage of instruments and background noise into the vocal channel are minimized.

Microphones

We had used various commercial microphones and found omnidirectional and continuously variable D types to have satisfactory sound characteristics (naturalness) for the vocals. But since it was our desire to exclude the instrumental sound from the vocal system we had a problem which could not be solved by a directional microphone because the instrument loudspeakers are located behind the vocalists on axis with the desired pickup. Therefore we turned to the dipole type in which the response is a function of the difference of the sound pressures at two distinct points. This configuration today (1975) is usually called a differential microphone, and as a close-talking microphone, the output is independent of frequency. This is a first-order gradient microphone and it possesses excellent antinoise characteristics. We place the pressure microphones about 60 mm apart. Wider separations reduce the effectiveness for higher frequencies and closer spacings can roll-off the low frequency in voice since the low frequencies of the vocalist can be heard by both microphones.

Our first implementation was with two dynamic microphones connected in series opposition. When the input impedance is much higher than the geneator impedance of the microphone, each can generate its voltage properly and excellent results are obtained. (We do not recommend the reverse-polarity parallel connection as the inductance of the second microphone will attenuate the low frequencies of the vocal microphone in the same manner as a "voice" response inductor which is switchable in many microphones to roll off the bass response.) Often, splitter connections must be made to the microphones for recording and live broadcasting and under these conditions, the simple connection shown which offers a relative independence of loading effects. By this time we had achieved pretty good rejection of our instrument sound field but we felt that with closer matched microphones we could do even better.

We tried condenser measuring microphones from various manufacturers but found only one which would give us better matching than the dynamic microphones. For the final system, we asked this manufacturer to select a series of elements matched in amplitude and phase and obtained elements with amplitude match better than ± 0.1db and phase match better than 1 degree at 10KHz! This precise match made our noise canceling performance outstanding and the sound quality of the microphone for music is unexcelled. We used preamplifiers designed to use the measuring microphone elements with an instrumentation tape recorder but modified them for greater dynamic range.

All the direct (vocal) microphones were resistively summed and all the ambiance (noise canceling) microphones were resistively summed and then the difference was taken by an ultra low distortion amplifier. No conventional gain controls were used and thus the signal path was kept as clean as possible. The sensitivity of the microphones is controlled by varying the polarizing voltage applied to the condenser element. The same voltage is applied to both microphones of the differential pair, preserving the noise-cancelling capability.

A control is mounted on as small box which serves as the mounting structure for the microphone. This control permits the performer to control the output of his microphone. Provisions are also made to remotely control the sensitivity when announcements are being made by persons unfamiliar with the system. On the remote control panel is a switch for each microphone which convert it to an omnidirectional microphone by bypassing the ambiance element.

For recording and broadcasting, each microphone is provided with separate difference amplifiers which has two transformer isolated outputs. Each microphone may then be recorded on a separate track.

Because of the antinoise characteristics of the microphones, the sensitivity drops off rapidly when one moves away from the element. This causes some problems for first-time users who must not wander around as they may be accustomed to with conventional microphones. There are those who reject the microphones for this reason. Heaters should be provided for the microphones since considerable condensation from the breath can load the diaphragm and destroy the match of the elements.

The Piano System

This is a small version of the vocal system. In this case a crossover divides the frequency range into three parts. The highs and mids go through a cluster of 5 and 12 inch speakers built in the same fashion as the vocals center cluster. The lows go through a column of 15 speakers. There is a separate volume control for each of the five Countryman custom pickups (one for each division of the frame) so Godchaux can balance the sound. Garcia and Kreutzman both have piano monitors or fills in their areas of the stage, which can be independently adjusted by them.

The piano system is smaller than the vocal system but configured very similarly. The pickup is by means of condenser elements suspended above the strings of the grand piano which function similaryly to the condenser microphones. This pickup system was developed by Carl Countryman Assoc. with Dan Healy.

A noise problem (hiss) was first attached with keyed amplifiers installed after the crossover networks, but we found that the playing of a soft note would open the hiss for an entire band and this hiss was sometimes subjectively lounder than the note. The problem was solved with the use of a dynamic noise filter by Burwen which functions superbly in this application.

The Drum System

\The drum system has two independent parts. The bass drum uses one amplification channel and sixteen 15 inch speakers in a column. The other drums and cymbals are miced through a three-way crossover which separates the signal into Highs, Upper Mids and Lower Mids and feeds them to tweeters, 5 inch and 12 inch speakers. This second part of the drum system uses two channels as it is stereo with identical speaker columns on both sides.

This system was basically built with leftovers from other parts of the system (the drums had previously been mixed into the vocals system).

Jerry is using a Doug Irwin/Alembic custom guitar. It has a Gibson Les Paul type body with a Fender Stratocaster pickup.

Bob currently plays a Gibson 335 guitar. He uses such special instruments as an Eventide Clockwork Digital Delay unit for repeating notes and creating an echo-like delay of different sound colorations and textures. A Eventide Clockwork work phaser system, an Orban/Parasound studio reverberation unit. Another accessory is an Alembic Parametric Equalizer (a flexible tone circuit) which gives him complete control of frequency responses by enabling boost or cut adjustments at any or all of three band-widths. The sharpness of the boost or cut can also be controlled

Each of the two guitar systems is a single full range column of twelve inch transducers. Due to the nature of guitar sounds, only about 5% of the power required for the vocals. Both guitar systems utilize a single power amplifier of the type used in the rest of the system.

The Electric Bass

Phil is using a new quadraphonic bass, the electronics of which were designed and built by George Mundy and the body and pickups by Rick Turner. The new bass has the same versatile qualities as the old bass: three pickups (bass and treble pickups covering all the strings, and a quad pickup which has a separate signal for each string); on each of the bass and treble pickups there are controls which enable him to select 1) the band-width of the filter, 2) the center frequency of the filter, 3) the kind of filter being used and 4) mix unequalized unfiltered direct sound with the filtered sound. The variety of sounds which can be achieved on the bass is the result of the many different combinations of these variables which can be used. The new bass has a frequency response with a crisper tone, and two quad pickups instead of one, the new one being a frequency-detector pickup. The main addition to the new bass is a Digital Decoding Circuit such that ten push buttons on the bass allow Phil to select any one of sixteen quad spatial arrangements of his speakers, and eight in stereo mode

The bass guitar system has two columns of fifteen inch tranducers stacked 18 high. Four power amplifiers are used as the bass requires more power for equal loudness. Since teh instrument has the capability to operate with individual outputs on each of the four strings, the array can be fed in this manner which makes it possible to play chords on the bass without intermodulation.

Designers and Workshops

The Grateful Deads sound system has evolved over the last eight years as a technical and group enterprise, a sort of logical accumulation of speakers and people. Changes have been made continuously in all directions which aid in improving the quality of the sound, both which the audience hears and which the band has to work with on stage. The concept and design of the current system/level was worked out by Bear, Dan Healy and Mark Raizene of the Deads sound and equipment crew, and by Ron Wickersham and Rick Turner of the Alembic sound company. The construction and regular maintenance is done at the Deads technical workshops by the people responsible for managing and transporting the system on the road. The design and construction of some special electronic components was done at Alembic, where John Curl is a consultant to the project

The number of people going on the road to handle all the sound equipment, lights, scaffolding and staging varies, but a typical configuration is: band - 6, sound - 10, lights - 4, staging and trucking - 7, road management - 3. The sound system travels in a 40 foot semi, staging and scaffolding on two flatbed semis and the lights in a 24 foot van. All this weighs about 75 tons.